The present invention relates to an air-fuel ratio controlling apparatus for internal combustion engines, or more in particular to an air-fuel ratio controlling apparatus for internal combustion engines in which the amount of the current supplied to a pump cell of an exhaust gas sensor is controlled thereby to set a target air-fuel ratio at an air excess side of the stoichiometric air-fuel ratio by feedback control.
An exhaust gas sensor for detecting the oxygen in the exhaust gas is disclosed in U.S. Pat. No. 4,272,329. The exhaust gas sensor of this type requires a small aperture for introducing the exhaust gas and has the disadvantage that, when installed in the exhaust pipe, is clogged with carbon or the like, thus making accurate measurement impossible.
An exhaust gas sensor of closed type free of the above-mentioned disadvantage is disclosed in Japanese Patent Publication No. 34058/81. In this type of exhaust gas sensor, it is decided only whether or not the mixture gas is rich or lean as compared with a predetermined air-fuel ratio. This type of sensor is also such that a predetermined current continues to be supplied to a pump cell for setting the oxygen concentration of a reference gas, and therefore the detection of the oxygen concentration is likely to develop an error.